Commit cecbca96 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

tracing: Dump either the oops's cpu source or all cpus buffers

The ftrace_dump_on_oops kernel parameter, sysctl and sysrq let one
dump every cpu buffers when an oops or panic happens.

It's nice when you have few cpus but it may take ages if have many,
plus you miss the real origin of the problem in all the cpu traces.

Sometimes, all you need is to dump the cpu buffer that triggered the
opps, most of the time it is our main interest.

This patch modifies ftrace_dump_on_oops to handle this choice.

The ftrace_dump_on_oops kernel parameter, when it comes alone, has
the same behaviour than before. But ftrace_dump_on_oops=orig_cpu
will only dump the buffer of the cpu that oops'ed.

Similarly, sysctl kernel.ftrace_dump_on_oops=1 and
echo 1 > /proc/sys/kernel/ftrace_dump_on_oops keep their previous
behaviour. But setting 2 jumps into cpu origin dump mode.

v2: Fix double setup
v3: Fix spelling issues reported by Randy Dunlap
v4: Also update __ftrace_dump in the selftests
Signed-off-by: default avatarFrederic Weisbecker <>
Acked-by: default avatarDavid S. Miller <>
Acked-by: default avatarSteven Rostedt <>
Cc: Ingo Molnar <>
Cc: Thomas Gleixner <>
Cc: Li Zefan <>
Cc: Lai Jiangshan <>
parent b15c7b1c
......@@ -789,8 +789,12 @@ and is between 256 and 4096 characters. It is defined in the file
as early as possible in order to facilitate early
boot debugging.
[FTRACE] will dump the trace buffers on oops.
If no parameter is passed, ftrace will dump
buffers of all CPUs, but if you pass orig_cpu, it will
dump only the buffer of the CPU that triggered the
[FTRACE] Limit the functions traced by the function
......@@ -1337,12 +1337,14 @@ ftrace_dump_on_oops must be set. To set ftrace_dump_on_oops, one
can either use the sysctl function or set it via the proc system
sysctl kernel.ftrace_dump_on_oops=1
sysctl kernel.ftrace_dump_on_oops=n
echo 1 > /proc/sys/kernel/ftrace_dump_on_oops
echo n > /proc/sys/kernel/ftrace_dump_on_oops
If n = 1, ftrace will dump buffers of all CPUs, if n = 2 ftrace will
only dump the buffer of the CPU that triggered the oops.
Here's an example of such a dump after a null pointer
dereference in a kernel module:
......@@ -289,7 +289,7 @@ static struct sysrq_key_op sysrq_showstate_blocked_op = {
static void sysrq_ftrace_dump(int key, struct tty_struct *tty)
static struct sysrq_key_op sysrq_ftrace_dump_op = {
.handler = sysrq_ftrace_dump,
......@@ -492,7 +492,9 @@ static inline int test_tsk_trace_graph(struct task_struct *tsk)
return tsk->trace & TSK_TRACE_FL_GRAPH;
extern int ftrace_dump_on_oops;
enum ftrace_dump_mode;
extern enum ftrace_dump_mode ftrace_dump_on_oops;
#define INIT_TRACE_RECURSION .trace_recursion = 0,
......@@ -490,6 +490,13 @@ static inline void tracing_off(void) { }
static inline void tracing_off_permanent(void) { }
static inline int tracing_is_on(void) { return 0; }
enum ftrace_dump_mode {
extern void tracing_start(void);
extern void tracing_stop(void);
......@@ -571,7 +578,7 @@ __ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap);
extern int
__ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap);
extern void ftrace_dump(void);
extern void ftrace_dump(enum ftrace_dump_mode oops_dump_mode);
static inline void
ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3) { }
......@@ -592,7 +599,7 @@ ftrace_vprintk(const char *fmt, va_list ap)
return 0;
static inline void ftrace_dump(void) { }
static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
#endif /* CONFIG_TRACING */
......@@ -117,9 +117,12 @@ static cpumask_var_t __read_mostly tracing_buffer_mask;
* It is default off, but you can enable it with either specifying
* "ftrace_dump_on_oops" in the kernel command line, or setting
* /proc/sys/kernel/ftrace_dump_on_oops to true.
* /proc/sys/kernel/ftrace_dump_on_oops
* Set 1 if you want to dump buffers of all CPUs
* Set 2 if you want to dump the buffer of the CPU that triggered oops
int ftrace_dump_on_oops;
enum ftrace_dump_mode ftrace_dump_on_oops;
static int tracing_set_tracer(const char *buf);
......@@ -139,8 +142,17 @@ __setup("ftrace=", set_cmdline_ftrace);
static int __init set_ftrace_dump_on_oops(char *str)
ftrace_dump_on_oops = 1;
return 1;
if (*str++ != '=' || !*str) {
ftrace_dump_on_oops = DUMP_ALL;
return 1;
if (!strcmp("orig_cpu", str)) {
ftrace_dump_on_oops = DUMP_ORIG;
return 1;
return 0;
__setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
......@@ -4338,7 +4350,7 @@ static int trace_panic_handler(struct notifier_block *this,
unsigned long event, void *unused)
if (ftrace_dump_on_oops)
return NOTIFY_OK;
......@@ -4355,7 +4367,7 @@ static int trace_die_handler(struct notifier_block *self,
switch (val) {
case DIE_OOPS:
if (ftrace_dump_on_oops)
......@@ -4396,7 +4408,8 @@ trace_printk_seq(struct trace_seq *s)
static void __ftrace_dump(bool disable_tracing)
static void
__ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode)
static arch_spinlock_t ftrace_dump_lock =
......@@ -4429,12 +4442,25 @@ static void __ftrace_dump(bool disable_tracing)
/* don't look at user memory in panic mode */
trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
printk(KERN_TRACE "Dumping ftrace buffer:\n");
/* Simulate the iterator */ = &global_trace;
iter.trace = current_trace;
iter.cpu_file = TRACE_PIPE_ALL_CPU;
switch (oops_dump_mode) {
case DUMP_ALL:
iter.cpu_file = TRACE_PIPE_ALL_CPU;
iter.cpu_file = raw_smp_processor_id();
goto out_enable;
printk(KERN_TRACE "Bad dumping mode, switching to all CPUs dump\n");
iter.cpu_file = TRACE_PIPE_ALL_CPU;
printk(KERN_TRACE "Dumping ftrace buffer:\n");
* We need to stop all tracing on all CPUS to read the
......@@ -4473,6 +4499,7 @@ static void __ftrace_dump(bool disable_tracing)
printk(KERN_TRACE "---------------------------------\n");
/* Re-enable tracing if requested */
if (!disable_tracing) {
trace_flags |= old_userobj;
......@@ -4489,9 +4516,9 @@ static void __ftrace_dump(bool disable_tracing)
/* By default: disable tracing after the dump */
void ftrace_dump(void)
void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
__ftrace_dump(true, oops_dump_mode);
__init static int tracer_alloc_buffers(void)
......@@ -256,7 +256,8 @@ trace_selftest_startup_function(struct tracer *trace, struct trace_array *tr)
/* Maximum number of functions to trace before diagnosing a hang */
#define GRAPH_MAX_FUNC_TEST 100000000
static void __ftrace_dump(bool disable_tracing);
static void
__ftrace_dump(bool disable_tracing, enum ftrace_dump_mode oops_dump_mode);
static unsigned int graph_hang_thresh;
/* Wrap the real function entry probe to avoid possible hanging */
......@@ -267,7 +268,7 @@ static int trace_graph_entry_watchdog(struct ftrace_graph_ent *trace)
printk(KERN_WARNING "BUG: Function graph tracer hang!\n");
if (ftrace_dump_on_oops)
__ftrace_dump(false, DUMP_ALL);
return 0;
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